Job-site sizing
Air scrubber sizing calculator
Enter the work area and your target air changes per hour. The calculator returns the airflow you need and how many units of a given size to set up, after a realistic allowance for filter and duct losses.
Not sure what target to use? See recommended air changes per hour by room type.
- Room volume
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- Effective airflow
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- Air changes per hour
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- 99% of particles removed in
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- 99.9% removed in
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How to size air scrubbers for a job
- Measure the space you will treat — the containment, not the whole building. Volume is length × width × ceiling height.
- Pick a target ACH. Negative-pressure containments are commonly run at a minimum of 4 air changes per hour, a figure inherited from asbestos abatement practice; many remediators target 6 or more for mold and heavy dust. Fire and smoke odor work often runs higher still. See targets by job type.
- Derate the rated CFM. Manufacturer ratings are usually free-air with fresh filters. Loaded HEPA filters and lay-flat duct can take 20–30% off.
- Round up, not down. If the math says 1.3 units, you need 2 — or a bigger unit.
A 20 × 15 ft basement with an 8 ft ceiling is 2,400 ft³. At 6 ACH it needs 6 × 2,400 ÷ 60 = 240 CFM of effective airflow. One 500 CFM scrubber derated by 20% delivers 400 CFM, or 10 ACH — comfortably enough.
The same target in a 60 × 40 ft warehouse bay with a 12 ft ceiling (28,800 ft³) needs 2,880 CFM: eight 500-CFM units, or four 1,000-CFM units.
Negative pressure
When a scrubber exhausts outside the containment it becomes a negative air machine: it pulls more air out than leaks in, so contaminated air does not escape to the rest of the building. A differential of about −0.02 inches of water column (−5 Pa) is the figure most commonly cited. The ACH you calculate here is the exhaust airflow through the containment — tighter enclosures reach the target pressure with less airflow, leaky ones need more. More on the difference.
Size classes
| Rated airflow | Typical use | Notes |
|---|---|---|
| 300–550 CFM | Single rooms, small containments, crawlspace sections | Light, often stackable; easy to carry upstairs. |
| 600–1,000 CFM | The restoration workhorse: bedrooms to open-plan floors | Most common class for mold and water jobs. |
| 1,000–2,000 CFM | Large containments, commercial and construction dust control | Heavier; check the circuit amperage before running several. |
What to compare when buying
- Filtration stages — pre-filter, intermediate, and a true HEPA final filter (99.97% at 0.3 µm). Add carbon for odor.
- Variable speed — lets one unit run quietly as a scrubber or at full power for negative air.
- Ducting collar — needed for negative air setups; check the diameter matches your duct.
- Amp draw — several units on one 15 A circuit is a common job-site trip.
- Filter cost — the HEPA filter is the running cost; price replacements before buying the unit.
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